The present invention relates generally to the field of power amplifiers and to sine wave generators and, more particularly, to the field of high power radio transmitters and to very low frequency (VLF) transmitters.
For instance, the United States Navy operates strategic VLF (15-30 Khz) communication stations which transmit megawatts of power. These stations are now relatively outdated, inefficient, and costly to maintain. Motivation exists to replace these stations with a more efficient and less costly to maintain technology.
The field of solid state power conversion has become quite active in the last several years because of improved components, improved circuits, and new methods of modeling and analysis. Several techniques in this field are applicable to VLF applications. First, it is recognized that a switching mode amplifier configuration can be derived for every switching mode power conversion configuration. These configurations can be divided into those that require only one on-off transition per switch for a given frequency and those that require more than one. The latter suffer from the disadvantage of power losses which are directly related to the number of on-off transitions of the power switch. The single transition circuits include the conventional class D push-pull amplifier, resonant converters and vector summation converters. Resonant converters have the problem of difficulty in changing frequencies. Vector summation converters have an advantage over the class D configuration due to their potential ability to eliminate the need for regulating input power, their ease of accommodating any type of modulation, and their potential for reducing or eliminating output resonant circuitry.